Take into account that a women will not be able to handheld the Mamiya DF camera for more than 60 seconds.
The Mamiya with two sets of batteries, lens and digital back is much heavier than a complete H4D camera with a lens of similar focal length.
Your choice is easy, if you want to share equipment with another photographer.
I am sorry, this is incorrect.
1.78 KG/3 lbs, 1 Oz - H4D-60 Body, Back, Grip
2.3 KG/5 lbs, 1 Oz - H4D-60 Body, Back, Grip, 80mm HC Lens
1.86 KG/4 lbs, 2 Oz - DF Body, P40+ Back, Grip
2.38 KG/5 lbs, 4 Oz - DF Body, P40+ Back, Grip, 80mm LS Lens
1.9 KG/4 lbs, 3 Oz - DF Body, IQ180+ Back, Grip
2.42 KG/5 lbs, 5 Oz - DF Body, IQ180+ Back, Grip, 80mm LS Lens
With the lens, the systems are within a few ounces of each other. The Phase/Schneider lenses generally weigh less than their Hasselblad counterparts, so unless the female photographer was intending to shoot without a lens, her support strain will be equivalent with either system.
Not discussing the back, is there a real difference in quality?
Would it be worth it to not get the Mamiya add-on when buying a Phase or Leaf Credo, finding a used H1 or H2 and than upgrading to a H4x?
As far as mixing systems, the Leaf and H4X issues are well documented. However, we rent Phase One DB's on H4X cameras all the time, and they work the same way they do on an H1 or H2 camera (operationally). I too am somewhat cautious about mixing and matching systems. However, I feel it is more of an issue with short term upgrading options. If you're the type who intends to use for 3-5-7 years on a system, if it has a track record of working well, I think you're ok, in general. We don't have too many issues with Leaf or Phase users on Contax or Hasselblad V platforms, for example.